The invention relates to a switching matrix for telecommunication exchanges, in which an input conductor is optionally connectable to an output conductor by means of a change-over switch comprising a selecting circuit for actuating the change-over switch in response to a junction selection signal to be applied to the selecting circuit.
A change-over switch for such a switching matrix is known from the periodical "IEEE Journal of Solid State Circuits", Vol. SC-13, No. 2April 1978, pp. 258-261, especially FIG. 1.
The change-over switch described in the above correspondence comprises an amplifier section for analog signal transmission, and a selecting circuit. The amplifier section is constituted by a base-driven input transistor in whose collector line the input to a current mirror is realized. The output of this current mirror is serially connected to a diode-switched transistor whose emitter is connected to the emitter of the input transistor. The anode of the diode formed thus constitutes the signal output of the change-over switch.
The selecting circuit of this known change-over switch is formed by a current source which is serially interrruptably connected to the two emitters.
This known change-over switch is designed for switching through analog signals. The frequency band of this change-over switch for these signals stretches out to approximately 800 MHz; it further appears from the said pulication that when this change-over switch is actuated, there is a delay of approximately 5 ns and a rise time/fall time of approximately 10 ns.
Furthermore, the current which can be supplied to the load impedance by this change-over switch is limited to a maximum of the current flowing through the serially connected current source. Consequently, only a limited voltage swing over the output impedance is possible.